the x key as gone?

Do you mean an ER-A420? You normally can't lose the X button as it is allocated straight after a RAM clear (MRS). Try a no sale in REG mode before you turn the key for programming and see if that makes a difference.

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If anyone needs more information, the Sharp ER-A420 manual is here:

http://the-checkout-tech.com/manuals/cashregisters/Sharp6.php

Registerman
June 2012